Waterborne Polyester Primer Basecoat Clearcoat 3-Wet Curing
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Solution Overview
Problem
The existing 3-wet paint systems for automotive coatings face challenges such as interfacial bleeding, aesthetic appearance issues, and reduced chip resistance, which hinder their commercialization, and require reformulation of clearcoats to prevent intermixing with basecoats, especially when using metallic pigment flakes.
Innovation Solution
A method involving the application of a waterborne primer and basecoat composition followed by a clearcoat, using a water-soluble or water-dispersible polyester with specific monomer ratios, allowing for simultaneous wet-on-wet-on-wet application and curing, which enhances film properties and prevents intermixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional cured primer composition is used to provide a smooth surface and prevent intermixing, then strike-in resistance and surface smoothness are improved, but the process complexity and equipment requirements increase due to separate primer booths and ovens
Solution Approach 1:
The patent merges the primer, basecoat, and clearcoat application processes into a single wet-on-wet-on-wet operation, eliminating the need for separate primer booths and ovens. The polyester resin system enables all three layers to be applied wet and then cured simultaneously in a single bake cycle, while still preventing intermixing and maintaining strike-in resistance.
Solution Approach 2:
The polyester resin serves multiple functions: it provides the film-forming binder for the waterborne primer and basecoat compositions, enables wet-on-wet application without intermixing, and allows simultaneous curing with the clearcoat. This multi-functional resin system replaces the need for separate curing equipment for the primer layer.
2Reliability
If separate primer booths and ovens are used to cure the primer before applying basecoat and clearcoat, then intermixing is prevented and appearance is maintained, but VOC emissions and CO2 emissions increase
Solution Approach 1:
The patent changes the chemical composition parameters by using a waterborne polyester resin system with specific molecular weight and functional group characteristics. This enables the primer and basecoat to remain stable in wet conditions during simultaneous application, allowing the entire coating system to be cured in a single bake cycle with reduced emissions.
Solution Approach 2:
The patent extracts and eliminates the separate primer curing step from the traditional multi-stage process. By using the specialized polyester resin system, the primer layer can be applied wet and then cured simultaneously with the other layers, removing the need for a dedicated primer oven and reducing overall emissions.
3Object-generated harmful factors
If waterborne coating compositions are used to reduce solvent content and emissions, then environmental impact is reduced, but interfacial bleeding and chip resistance become significant concerns
Solution Approach 1:
The patent uses a composite polyester resin system with specific characteristics (molecular weight 5,000-50,000, specific functional groups) that combines the benefits of waterborne formulations with the performance characteristics of traditional solventborne systems. This composite material approach maintains chip resistance while enabling reduced emissions.
4Reliability
If clearcoat is reformulated to resist intermixing with basecoat in 3-wet systems, then aesthetic appearance is improved, but device complexity and formulation complexity increase
Solution Approach 1:
The patent changes the chemical parameters of the polyester resin to enable wet-on-wet-on-wet application without requiring clearcoat reformulation. The specific molecular weight range and functional group composition of the polyester provide the necessary stability and compatibility, simplifying the overall formulation while maintaining aesthetic appearance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method improves the appearance and chip resistance of the coating system while reducing environmental impact by eliminating the need for separate primer booths and ovens, achieving cost savings and better film properties through the use of a waterborne polyester in the primer and basecoat compositions.
Implementation Method 1
a polyester which is water soluble or water dispersible and is the reaction product of a monomer mixture
Implementation Method 2
a polyester which is water soluble or water dispersible
Implementation Method 3
heating the applied layers of coating composition to cure the applied layers
Implementation Method 4
curing of all three applied layers
Data Source
AI summary
The present disclosure is directed to a method of applying at least one layer of a waterborne primer composition, at least one layer of a waterborne basecoat composition and at least one layer of a clearcoat composition to a substrate followed by a heating step which simultaneously cures the applied layers of coating composition.